62 On the Navigation of Cape Horn. 



He, who in the China seas, is warned by the barometer, of the 

 approaching Typhoon, and can foretell the coming of a gale by the 

 height of the mercury in it, finds that off Cape Horn, the same indi- 

 cations are frequently followed by moderate breezes and even by 

 calms* Here the mercury, below the mean height of lower latitudes, 

 becomes very unsteady, falling and rising several inches in a few hours. 

 During the strength of a gale, sometimes it is observed to rise, at 

 other times it falls or remains in statu quo. Its mean height south of 

 the latitude of Cape Horn is 29*03 in. 



As the Pacific coast of Tierra del Fuego and Patagonia is ap- 

 proached with the wind from the westward, the mercury in the ba- 

 rometer ascends. When the wind is strong, it rises above thirty in- 

 ches, and close under the land with fresh westerly gales it frequent- 

 ly stands above 30-50 in. 



From lat. 45°, embracing a region towards the south of twelve 

 or thirteen degrees in breadth, the most prevalent winds are from 

 the westward. Vessels entering this region from the south have a 

 rise in the barometer, when the wind is on the land. The rise is 

 generally observed to commence about the latitude of the Cape, 

 continuing to increase as the land is neared; and when the winds 

 are fresh, a greater accumulation of atmosphere is shown by a high- 

 er range of the mercury. 



The result of my own barometrical observations compared with 

 others to which I have had access, shews that within this region, 

 the barometer stands higher when the winds are from the westward, 

 than it does, caeteris paribus, between the same parallels in the At- 

 lantic. The difference is nearly as twenty nine to thirty, and increases 

 as the land is approached. This accumulation of atmosphere is cau- 

 sed from the obstruction which the mountains of Patagonia, and the 

 highlands cf Tierra del Fuego affix to the winds in their passage 

 across the continent towards the Atlantic. The air thus obstructed is 

 compressed by that coming after it, and according to the force of the 

 wind, and the distance from the land, the barometer indicates a 

 greater or less superincumbent pressure. The disturbing cause which 

 first destroyed the atmospheric equilibrium towards the East, contin- 

 uing to act, the density of the obstructed air is increased by the in- 

 creased tendency to restore the equilibrium from the west. The 

 air thus forced, rushes around the southern extremity of the land, 

 with an impetuosity that is known only to those, who experience the 

 effects of its violence. This current of air, as it sweeps around 



